I think there is bigger picture to look at Fleet Movements wise outside of the Go North East Fleet as I think once the likes of East Yorkshire, Brighton & Hove, Southern Vectis, Salisbury Reds & Pulhams get there EV's into service in coming months there will be a larger group wide cascade plan.

Below is what is currently on order from what I have found for other Go-Ahead Subsidies.

East Yorkshire = 40 EV's on order
Brighton & Hove = 29 EV's on order
Southern Vectis = 31 EV's on order
Salisbury Reds = 23 EV's on order
Pulhams = 15 EV's on order

Total = 138 

CBA to count through how many Go-Ahead London have on order.